Angle-resolved photoelectron measurements on the first two orbitals of acetylene using synchrotron radiation

The angle-resolved photoelectron spectrum of acetylene has been measured using synchrotron radiation over a range of photon energies from 12 to 28 eV.     

Angle-resolved photoelectron spectroscopy of benzene and hexafluorobenzene as a function of photon energy

Angle-resolved photoelectron spectra of benzene have been recorded using synchrotron radiation as the photon source. From these results the angular dis the first three orbitals; 1e_1g(π), 3e_2g (σ) and 1a_2u(π). Calculations of β employing the MS Xα method have also b and theory for the first two orbitals is excellent. Poor agreement in the core of the third orbital is believed to be due to overlap of the second and has been verified by data obtained for perfluorobenzene. The universality of the energy dependence of β for π orbitals, noted previously for unsatu aromatic systems. The importance of the results for benzene for the future application of angle-resolved photoelectron spectroscopy to complex molecule     

Angular distribution of the photoelectron spectra for ethylene,propylene, butene and butadiene

The photoelectron spectra using the He I resonance line (21.22 eV) were measured for ethylene, propylene, 1-butene, cis-butene, trans-butene and 1,3-butadiene as a function of angle between the direction of the incoming photons and outgoing photoelectrons. From these data the angular parameter, β, is obtained for each photoelectron peak in each spectrum. The β value is a function of the energy of the photoelectron and the nature of the molecular orbital from which the photoelectron is ejected. A qualitative comparison is made between the experimentally derived β values and the molecular orbital assignments. In particular, it is noted that the photoelectron peak corresponding to the CC double bond π orbital yields a relatively high value of β. This has led in the case of butadiene to a confirmation that the first two photoelectron peaks both result from ionization in π orbitals.     

The He(I) photoelectron spectra of BrF and IF

The vacuum ultraviolet photoelectron spectra of BrF (X¹Σ⁺) and IF (X¹ Σ⁺) have been recorded and interpreted with the aid of both MS — Xα — SCF calculations and ab initio calculations. For both BrF and IF the first band is split by spin—orbit coupling into two components corresponding to ionization to the X²Π$\text{3}\text{2}$ Phytochemistry and X²Π$\text{1}\text{2}$ ionic states. Estimates of re, ?we and De for these states have been made.     

He(I) and He(II) photoelectron spectra of some substituted ethylenes

The He(I) and He(II) photoelectron spectra of acrolein, acrylic acid, methyl acrylate, vinyl acetate, acrylamide and some of their methyl-substituted analogues are reported. Detailed assignments are proposed, mainly based on differences in intensity between the He(I) and He(II) spectra, on sum rule considerations and on the results of modified CNDO/S calculations.The assignment criteria are critically evaluated.     

He(I) and He(II) photoelectron spectra of iron tetracarbonyl-olefin complexes

The He(I) and He(II) photoelectron spectra of a series of iron tetracarbonyl—olefin complexes (olefin = acrolein, crotonaldehyde, methyl acrylate, acrylic acid, dimethyl maleate and some dihalogenated ethylenes) are reported. Assignments are proposed, based on differences in intensity between the He(I) and He(II) spectra, in comparison with related compounds and the results of extended CNDO calculations. The electronic structure of the coordinated olefins is discussed.     

New method for photoelectron spectroscopy of solutions

A new method of rather general scope is reported for the determination of the photoionization (PI) spectra of solutions. Spectra thus obtained correspond to PI for ejection of quasi-free electrons into the liquid phase. The method is based upon photoelectron emission (PEE) into vacuum by the solution upon irradiation with adjustable photon energy. A new instrument is described which features irradiation (up to 10 eV) of a film of the solution on the rim of a rotating disk target (72 r.p.m.). Two types of data are obtained: PEE quantum yield per incident photon as a function of photon energy; energy distribution curve (EDC) of electrons emitted into vacuum at given photon energies. The PI cross-section is obtained as a function of photon energy by the previously developed method of EDC superposition. The method is applicable even when the contribution by the solvent to total PEE is dominant. Application is made to PI by 0.4 M indole in glycol for irradiation from 6.5 to 10 eV. Experimental results include: the effect of equilibrium vapor pressure (3.5 × 10^?3 ? 4.6 × 10^?2 torr) on EDC's; PEE spectral response of solvent and solution; EDC's from 6.5 to 10 eV. Interpretation covers these results and also includes: attenuation of the photon flux in the gas phase; PI in the gas phase; changes of temperature and solute concentration caused by evaporation. The PI spectrum of indole in glycol at ?7 °C exhibits a band for bound-continuum transitions (rising segment up to ≈ 7.0 eV) and a superimposed band (maximum at ≈ 7.6 eV) for PI via autoionization of excited bound states. Systematic development of the photoionization spectroscopy of solutions up to 10 eV is made possible by this approach. Application of the rotating disk methodology to higher photon energies (HeI, ESCA) may be of interest.     

New depth-profiling method by angular-dependent x-ray photoelectron spectroscopy

A non-destructive method for depth profiling by X-ray photoelectron spectroscopy, based on the dependence of the analysed depth with the electron emission angle, is presented.The extraction of the concentration profile from angular distribution experiments is achieved, in the framework of a flat-layer model, by minimizing the difference between theoretical and experimental relative intensities. The applicability and limitations of the method are discussed on the basis of computer simulation results. In particular, constraints reflecting the physical properties of the system must be introduced in the numerical treatments. The depth probed is of the order of 3λ, λ being the value of the inelastic mean free path, and the depth resolution is of the order of λ/3. In tests of the method, the concentration depth profiles of the Ag-Al₂O₃ and the SiO₂-Si interfaces and of the surface region of a Cu-Ni alloy have been obtained.     

Satellite phenomena in the X-ray photoelectron spectra of lanthanide trihydroxides

Using the direct CI method perturbation corrections to the Koopmans ionization energies have been obtained up to order 10 for the molecules CN^? and H₂O. The results are compared with those from the fully converged CI and B_k-type calculations. The convergence of the perturbation series is found to be quite slow although substantial improvement is possible using a variation-perturbation method.     

Ion-induced auger electron emission of Mg,Al and Si as a function of ion energy

Experiments have been performed in which ion-induced Auger electron yields of Mg, Al and Si were measured as a function of ion energy. A computer simulation based on a binary collision cascade model yielded results that were in close agreement with the experimental findings. From this a model is proposed, where the creation of inner shell vacancies occurs during symmetrical collisions in the collision cascade generated by the ion. From the minimum energy required for Auger emission a distance of closest approach between the particles can be derived, using the Molière approximation of the screened Coulomb potential to describe the collisions. This distance can be correlated with the radii of the interacting orbitals derived from Hartree-Fock-Slater calculations.     

Vibrational spectra of Matrix isolated binary and mixed cadmium dihalides

The Raman spectra CdX₂ and CdXY (X, Y = Cl, Br, I) molecules isolated in solid krypton at 20°K are reported together with the matrix isolation infrared spectrum of CdX₂ and CdXY (X, Y = Br, I) molecules. Isotopic effects and force constants are discussed and several irregularities in them are interpreted as possible indications of slightly bent structures. The bending vibration frequency of CdClI as well as several bands assigned to dimers are also reported.     

2D surface phonons in high-resolution electron-energy-loss spectra of metallic oxides

Surface phonon features in high-resolution electron-energy-loss (HREEL) spectra of the metallic tungsten bronze oxide Na_0.7WO₃ are much weaker than for insulating WO₃. Models based on the bulk dielectric function ?(ω) are unable to rationalise these spectra, but a simple two-layer model involving an unscreened surface dielectric layer is shown to account for both the intensities of the metallic phonons and their energies relative to those for WO₃. The sensitivity of HREELS to details of surface structure in metallic oxides is emphasised.     

The electronic structure,x-ray photoelectron and emission spectra of YOF

The results of electronic structure calculations for YOF are presented, making use of Xα-DVM together with experimental X-ray photoelectron and emission spectra for this compound. Three versions of calculations have been performed, depending on the relation between oxygen and fluorine charges in the [YO₄F₄] cluster. The interpretation of experimental spectra is carried out on the basis of these calculations.     

Dissipation energy for a charge moving near a metal surface

The energy dissipated by a moving charge approaching a metal has been obtained for a wide range of the incoming velocities. Regime limits for very small or very great velocities are analysed as particular cases, and some experimental evidence for the system He⁺/Au is discussed in the light of our results.     

X-ray photoelectron spectroscopy of TiO2 and other titanate electrodes and various standard Titanium oxide materials: Surface compositional changes of the TiO2 electrode during photoelectrolysis

Surface compositional changes were observed for TiO₂ single crystal electrodes used for photoelectrolysis of water. Surface stoichiometries of several types of TiO₂, SrTiO₃ and BaTiO₃ electrodes were characterized by XPS and compared with a variety of titanium, titanium oxide and titanium hydride standard materials. Reduction of the electrode surface in a hydrogen atmosphere results in an oxygen deficient surface composition. Photoelectrolysis at current densities of $\text{10–15}\text{mA}\text{cm}{}^2$ for periods up to 8 h appears to return the electrode surface to a nearly stoichiometric oxygen-to-metal ratio. Reduction of the titanium oxide surfaces was also observed by exposure to an argon ion beam. Analysis of the electrode surface by a combination of XPS and ion-sputter profiling was still possible by simultaneous analysis of standard materials.